Immunity of the linear Mu genome in vitro. (a) Transposition reactions were set up by incubating MuA, MuB and HU proteins with the mini-Mu plasmid pSP104 as donor and either linear Mu genome or pUC19 as target, as described in Methods. Lane 1, cleaved Type I complex assembled on pSP104; lanes 2 to 4, Type II or strand transfer reactions with: pSP104 as donor and either pUC19 (lane 2) or Mu (lane 3) as target or Mu as donor and pUC19 as target (lane 4); lanes 5 to 7, control substrates without added proteins. (b) Map of pSP104 showing restriction enzyme sites used for linearization and their position with respect to the att L and att R Mu ends. (c) Transposition reactions with linear mini-Mu as target. Reaction conditions were as in (a), except that Type I complexes were first assembled on pSP104 and added to indicated targets in a second step. Lane1, Type I reaction; Lane 2 to 7, Type II reactions. Lanes 8 to 13, DNA controls without added proteins. Restriction enzyme shown in the B panel are abbreviated to H, X and B. L = linear. O = open circular; S = supercoiled; Type I = cleaved complex; Type II = strand transfer complex; Type II (intra) = intramolecular strand transfer complexes.